Derivative functions > Finding the derivative
1234Finding the derivative

Solutions to the exercises

Exercise 1
a

f ' ( x ) = 3 x 2 - 4 and f ' ( 1 ) = -1

b

g ' ( x ) = 4 x 4 + 6 x 2 - 10 x + 12 and g ' ( 1 ) = 12

c

s ' ( t ) = 60 - 9,8 t and s ' ( 1 ) = 50,2

d

H ' ( t ) = 4 t and H ' ( 1 ) = 4

e

d y d x = -2 x + 6 and y ' ( 1 ) = 4

f

P ' ( x ) = 3 a x 2 + 2 b x + c and P ' ( 1 ) = 3 a + 2 b + c

g

d T W d q = 1,5 q 2 - 12 q - 25 and T W ' ( 1 ) = 35,5

h

K ' ( x ) = 9 a x 2 - 6 x - 3 a 2 and K ' ( 1 ) = 9 a - 6 - 3 a 2

Exercise 2
a

f ' ( x ) = 2 x 3 - 8 x and f ' ( x ) = 0 as x = 0 x = ± 2 , so ( 0 , 0 ) , ( -2 , -8 ) and ( 2 , -8 ) .

b

T W ' ( q ) = -3 q 2 + 6 q + 3 and T W ' ( q ) = 0 as q = 1 ± 2 , so ( 2,4 ; 16,7 ) and ( -0,4 ; 5,3 ) .

c

v ' ( t ) = 3 t 2 - 4 t + 1 and v ' ( t ) = 0 as t = 1 3 t = 1 , so ( 1 3 , 4 27 ) and ( 1 , 0 ) .

d

T W ' ( p ) = 40 - 0,04 p and T W ' ( p ) = 0 as p = 1000 , so ( 1000 , 20000 ) .

Exercise 3
a

f ( x ) = ( x 2 - 4 ) ( x 2 - 9 ) = 0 gives you x 2 = 4 x 2 = 9 and x = ± 2 x = ± 3 , so ( ± 2 , 0 ) en ( ± 3 , 0 ) .

b

f ( x ) = x 4 - 13 x 2 + 36 and f ' ( x ) = 4 x 3 - 26 x .

c

Tangent for x = - 2 is y = 20 x + 40 .
Tangent for x = 2 is y = - 20 x + 40 .
Intersect ( 0 , 40 ) .

d

f ' ( x ) = 0 if x = 0 x = ± 8,5 .

e

It allows you to find the three extrema: max. f ( 0 ) = 36 , min. f ( - 8,5 ) = -6,25 and min. f ( 8,5 ) = -6,25 .

Exercise 4
a

h ( 0 ) = 0,5 m.

b

h ' ( x ) = -0,02 x + 0,2 and h ' ( 0 ) = 0,2 m/s

c

It is the speed with which the height of the object changes at x = 0 . It is therefore not the initial speed of the object itself!

d

h ' ( x ) = 0 gives you x = 10 , which corresponds to the point ( 10 ; 1,5 ) .

e

It is the speed with which the height of the trajectory changes that is 0 . But there is also a component of the speed in the forward direction.

Exercise 5
a

G T K ( q ) = 1200 q + 0,2 q

b

q = 0 ; when q = 0 you cannot determine the average cost.

c

min. A T C ( 77 ) 30,98

d

A T C 0,2 as q ( is the symbol for "infinitely large" ).
The production costs per unit are eventually changing with the (fixed) costs per article.

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